The invention relates to a positioning system as defined in the opening part of claim 1.
The invention further relates to an apparatus as defined in the opening part of claim 5.
An apparatus including such a positioning system is known from GB-B-1 429 882. The known apparatus is suitable for reading optical information carriers. For this purpose, the transducer has a radiation-sensitive detector which generates a read signal in response to the radiation reflected from or transmitted by the information carrier. The supporting means take the form of a slide which is driven by a motor via a transmission formed by a worm-and-rack combination. For such uses the motor is generally constructed as a brush motor. The cooperation of the drive member and the fine-positioning member in the positioning system should combine an accurate positioning of a read or write location on the data carrier with a short access time. For a short access time it is desirable that the transmission ration, which is defined as the ratio obtained by dividing the slide travel by the angular rotation of the motor. A drawback is then that friction in the slide drive and cogging will play an important part. Cogging is the effect that the motor tends to assume preferential positions. These effects may give rise to such large deviations between the position occupied by the transducer and a desired position that these can no longer be corrected by the fine-positioning member. It is then no longer possible to read or write information from/to the information carrier in a reliable manner.
It is an object of the invention to take a measure which allows a comparatively large transmission ratio in an apparatus of the type defined in the opening paragraph, without this leading to impermissibly large deviations in the position assumed by the transducer. To achieve this object the apparatus in accordance with the invention has the characteristic features defined in claim 5. To achieve this object the positioning system in accordance with the invention has the characteristic features defined in claim 1.
Since the drive voltage in the positioning system in accordance with the invention and in the apparatus in accordance with the invention also depends on the current consumed by the drive member a better reproducible response of the drive member to the control signal is obtained. As a result of this, the second part (the supporting means, for example the slide) follows the third part (the transducer or a part thereof) with greater precision, so that the corrections to be performed by the fine-positioning member can be smaller.
The orientation signal, which represents the position of the third part with respect to the second part, can be generated by means of a sensor, for example by means of a capacitive or an inductive sensor. However, the embodiment defined in Claim 2 is to be preferred. This embodiment does not require any additional components for the generation of the orientation signal.
An attractive embodiment of the apparatus in accordance with the invention is defined in Claim 3. It is also possible to select a greater value for the constant , than the value for the upper limit mentioned in this Claim. However, this entails the risk that the positioning system becomes unstable in the case of small excursions of the components of the signal combination means or of the drive member.
For controlling the drive member it may be desirable to utilize a driver across whose output terminals a voltage is available which is substantially symmetrical with respect to ground. In that case the current consumed by the drive member can be measured more accurately in the embodiment defined in Claim 4.
The reliability of the information recorded on the record carrier and the information reconstructed therefrom can be improved by means of the measures defined in claim 6.